import java.util.Scanner;

public class Main5{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        double v0 = in.nextDouble();
        double v1 = in.nextDouble();
        int t = in.nextInt();
        AccelerationCal ac = new AccelerationCal();
        double acceleration = ac.calAcceleration(v0, v1, t);
        System.out.println(acceleration);
    }
}

/* 请在这里填写答案 */
class AccelerationCal
{
    public double calAcceleration(double v0, double v1, int t){
        // 在这里实现这个函数
        double a = (v1-v0)/t;
        return a;
    }
}